Kinematics/Kinetics
What is the difference between kinematics and kinetics?
Kinematics: study of movement (5 parameters of displacement)
Kinetics: Study of forces
How do you determine which is the effort force and which is the resistance force in a given lever system?
The effort force (EF) causes the rotation (in the direction of net torque), this is the "winner"--> has the largest torque
The resistance force (RF) resists the rotation of EF "loser"
How do you determine the net effect of 2 or more forces in the same linear force system when those forces are applied to the leg-foot system?
There will be an "x" and "y" component that make up a parallelogram
How can a force produce translatory and rotary (torque) force simultaneously?
It can move in 3 dimensions
What type of lever do most of the muscles in the human body work as?
3rd class lever
What is a force?
A push or pull on an object
What would you advise a kid to help them open a door easier by themselves?
Put both hands on the door as far away from the hinge as possible and push with arms at shoulder height, this results in the angle of application as close to 90 degrees as possible
What is a compression force?
Joint compression creates contact between 2 contiguous joint surfaces
2 forces equal in magnitude and opposite in direction on different but touching objects (femur and tibia)
What is the effect at the knee joint of a muscle that: lies paralel the the leg-foot, lies perpendicular to the leg foot, lies at a 45 degree angle to the leg foot or lies at a 135 degree angle to the leg foot?
They will all have different lengths of their moment arms
Where is torque at its max?
When the force is as far from the joint axis (larger moment arm) as possible
Also, when force is perpendicular to the segment
What force is ALWAYS touching an object?
Gravity
What is the "advantage" to a lever with a mechanical advantage greater than 1?
Mechanical advantage= EA/RA
The larger lever arm of the EF allows for the magnitude of the effort to be less than the magnitude of the resistance with it still "winning" the effort force can be smaller than the resistance
If the mechanical advantage of the lever is LESS THAN 1 the magnitude of the effort force MUST always be larger than the resistance due to the effort acting through a smaller distance (moment arm)
What is a distraction force?
A force that "pulls" one segment away from the other (joint distraction)
Joint distraction creates tension in capsuloligamentous structures crossing a joint
Example: gravity acting on leg foot segment
If gravity acting on the leg foot segment creates a distraction force and/or shear force at the knee joint, what prevents the tibial plateaus and femur from separating or sliding on each other?
The joint capsule and ligaments prevent it from separating or sliding on each other
What happens to Fx when the angle of application is less than 90 degrees?
Compression
What would happen if the line of gravity for a person does not lie within the persons base of support?
They will have less stability
What is the mechanical advantage of a first class lever, second class and third class lever?
First class: we can't infer a mechanical advantage
Second class: Always has a mechanical advantage >1 because EF is further from the axis than RF
Third class: Never has a mechanical advantage because EF lies closer to the axis than RF
What is a Shear force?
Whenever a force lies parallel to contacting surfaces and potentially slides one surface on another
Sliding surfaces create FRICTION, but friction in human joints has little to no magnitude
Example: gravity on leg foot on footplate is parallel to the foot plate, it will be opposed by Friction between the leg foot and the footplate
What kind of muscle contraction is created if muscle is effort force?
Concentric muscle contraction
What happens to Fx when the angle of application is greater than 90 degrees?
Distraction
What are the classes of Levers? Give example of each one.
Class 1: The axis is in the middle and the EF and RF are on either side of the axis. Example: Head nodding up and down
Class 2: The axis is on one end and the EF is on the opposite end with the RF closer to the axis, EA>RA. Example: There are no actual 2nd class levers in the body but Raising up on toes can be considered a 2nd class lever
Class 3: The Axis os on one end and the RF is on the opposite end with the EF closer to the axis, EA<RA. Example: Biceps curl (eccentric movement)
What conditions have to be met for an object to be in complete equalibrium?
How can a manual force applied to a leg foot segment be manipulated to increase torque or to decrease torque produced by that force?
If you increase the moment arm (MA) you increase the torque, If you decrease the force (F) or MA you can decrease the Torque, changing planes can also increase/decrease the Torque
What kind of muscle contraction is created if muscle is resistance force?
Eccentric contraction
How are the force components Fx and Fy related to the moment arm?
Fy and the moment arm are directly proportional to each other
Fx is inversely proportional to both